Semiconductor devices and liquid crystal display devices are manufactured by a so-called photolithography technique for transferring a pattern formed on a mask onto a photosensitive substrate. The exposure apparatus used in this photolithography process has a mask stage that supports a mask and a substrate stage that supports a substrate, and it transfers the pattern of the mask to the substrate via a projection optical system while sequentially moving the mask stage and the substrate stage. In recent years, higher resolutions for projection optical systems have been in demand to handle the even higher integration of device patterns. The resolution of the projection optical system is higher the shorter the exposure wavelength used and the larger the numerical aperture of the projection optical system. For this reason, the exposure wavelength used in exposure apparatuses has become shorter year by year, and the numerical aperture of the projection optical system is also increasing. In addition, the mainstream exposure wavelength at present is 248 nm of a KrF excimer laser, but a shorter wavelength, 193 nm of an ArF excimer laser, is also coming into practical application. In addition, when exposure is performed, the depth of focus (DOF) is also important similar to the resolution. The resolution R and the depth of focus δ are expressed by the respective equations below.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
Here, λ is the exposure wavelength, NA is the numerical aperture of the projection optical system, and k1 and k2 are process coefficients. Based on Equation (1) and Equation (2), it is apparent that when the exposure wavelength λ is made shorter to increase the numerical aperture NA in order to increase the resolution R, the depth of focus δ becomes smaller.
When the depth of focus δ is too small, it is difficult to match the substrate surface to the image plane of the projection optical system, and there is concern that the focus margin during the exposure operation will be insufficient. Therefore, the liquid immersion method disclosed in Patent Document 1 noted below, for example, has been proposed as a method of essentially shortening the exposure wavelength and increasing the depth of focus. In this liquid immersion method, the space between the lower surface of the projection optical system and the substrate surface is filled with a liquid such as water or an organic solvent to form a liquid immersion region, and the fact that the wavelength of the exposure light in liquid becomes 1/n in air (n is a refractive index of the liquid, which is normally approximately 1.2 to 1.6) is used to increase the resolution while expanding the depth of focus to approximately n times.
Patent Document 1: the booklet of PCT International Publication No. WO99/49504
In any case, when performing exposure based on the liquid immersion method, it is important to supply liquid in a desired status to prevent deterioration of the pattern image formed on the substrate and maintain exposure accuracy.
When the temperature of the liquid of the liquid immersion region fluctuates, the refractive index of the liquid, for example, fluctuates, and the pattern image formed on the substrate deteriorates, so it is particularly important to supply the liquid onto the substrate at the desired temperature. In addition, for example, in the case of a configuration in which the detected light of the focus detection system that detects the surface position information of the substrate surface and the detected light of the alignment system for aligning the substrate pass through the liquid of the liquid immersion region, when the temperature of the liquid of the liquid immersion region fluctuates, the optical path of the detected light fluctuates, deterioration of detection accuracy is brought about, and consequently this leads to a decrease in exposure accuracy. In addition, when the temperature of the liquid of the liquid immersion region fluctuates, the substrate and/or the substrate stage thermally deform, and there is a possibility of this as well leading to decreases in exposure accuracy and alignment accuracy. In addition, the pattern image formed on the substrate will also deteriorate due to bubbles being present in the liquid of the liquid immersion region and bubbles adhering to the lower surface of the projection optical system and/or the substrate surface.
In addition, it is also important to recover the liquid in a desired status to maintain exposure accuracy. When the liquid cannot be recovered well, there is a possibility of the various measurement operations relating to exposure processing being affected and of causing exposure accuracy to decrease due to the liquid flowing out and causing rust to occur in the peripheral mechanical components, bringing about fluctuation in the environment (humidity, etc.) where the substrate is placed, and causing changes in the refractive index on the optical path of the measurement light of the optical interferometer, used in stage position measurement. In addition, for example, when vibration is produced in the liquid recovery mechanism, there is a possibility that the vibration will cause deterioration of the pattern image projected onto the substrate and will bring about measurement errors of the interferometer that monitors the position of the substrate stage that holds the substrate.